Faults within circuitry such as memories can be repaired subsequent to manufacture by the use of redundant circuit elements that can be selected by fuse programmable logic to replace the faulty elements. The redundant elements have a cost of circuit area but they do enable production yields of circuits to increase as they allow circuits with some faults to still function correctly.
With the ever decreasing size of circuit elements, faults within them are becoming more likely such that the ability to be able to repair them using fuses is important.
Fuses can take the form of laser programmable fuses that are programmed by vaporising material with a laser, or electrically blown fuses which are programmed by passing a high current through them.
Electronic or E fuses are also known that store a repair signature that identifies a faulty element in a memory, for example, and provides it with an alternative storage address within reconfiguration registers. Thus, data is no longer stored in the faulty element rather it is stored in the redundant location that is identified by the E fuse data. In a system with many memories the size of the fuse box is directly related to the sum of the number of reconfiguration registers for each memory under test.
FIG. 1 shows a Built-In Test and Repair solution for an embedded memory. When repair is desired the controller 6 reads memory repair information from a fusebox 2 via a serial register 4. The Laser Fuse contents are first loaded into the serial shift registers and then serially shifted into the BIST/R controller. The fusebox 2 stores repair information for all of the memories associated with the controller 6. It is becoming common to control many memories, possibly up to 100 with a single controller, thus the amount of data stored in the fusebox is very large.
U.S. Pat. No. 6,577,156 discloses a fuse box in which the repair data is stored in compressed form within the fusebox. When the system wants to use the data, the data is decompressed using a decompressor within the fusebox and is then shifted out to various fuse programmable macros where the data is used to remove faulty memory locations.
U.S. Pat. No. 6,768,694 discloses memory elements within a chip that has a plurality of fuses connected to the memory elements that can be programmed to replace defective memory elements and a fuse controller for programming the fuses.